The present invention relates generally to safety devices primarily for use on oil drilling derricks on oil platforms or rigs, and is particularly concerned with apparatus when a traveling block approaches the top or crown block of a hoisting assembly on a drilling derrick or a hoisting unit.
Oil drilling derricks typically have hoisting equipment including a crown block at the top of the derrick and a traveling block which is linked to the crown block via a cable and pulley or sheave arrangement, and which travels up and down the derrick by means of a suitable hydraulic drive or the like Because of the large size and weight of the traveling block, the pulleys or sheaves in the crown and traveling block are liable to be damaged if the traveling block travels up far enough to strike the crown block. Additionally, debris as a result of such an impact may fall and possibly injure workers on the platform below. A number of devices have been used in the past to attempt to avoid such problems, but these are subject to various disadvantages.
Typically, to avoid the traveling block striking the crown block, a pair of wooden studs or rails is bolted across the derrick below the crown block, so that the traveling block strikes these rails before it reaches the crown block. However, these have a tendency to be crushed or separated from the derrick on impact, and often fall to the floor or platform, potentially injuring personnel.
Prior art which is incorporated by reference herein includes U.S. Pat. No. 5,838,246 for a safety device for a derrick with an alarm mechanism and related drilling derrick assemblies, such as U.S. Pat. No. 4,831,795, a dual cluster crown block as in U.S. Pat. No. 4,796,863, and a derrick with upper and lower crown blocks as in U.S. Pat. No. 4,903,443.
The present invention relates to a safety apparatus for a lifting structure having a crown and at least one traveling block, comprising: at least two support beams attached to crown of the lifting structure; a plate secured between the support beams; a bumper pad secured to the plate and adapted to be positioned at the crown of the lifting structure to cushion any impact with the traveling block if the traveling block is lifted towards the crown without stopping.
The invention also relates to an oil drilling rig apparatus, comprising: a derrick having a lower end for mounting on a platform, an upwardly projecting frame, and an upper, crown end; a traveling block suspended from the upper crown end within the derrick frame; drive means linked to the traveling block for driving the traveling block up and down the frame in a predetermined travel path; and a crown bumper comprising: at least two support beams attached to the derrick; a plate secured between said support beams; a bumper pad secured to the plate and adapted to be positioned at the crown end of the derrick to cushion any impact with the traveling block if it is pulled to the crown end without stopping.
The invention also relates to a method of preventing damage to the crown of a derrick at an oil drilling derrick prior to impact of a traveling block with a crown end of the derrick, comprising the steps of: securing a crown bumper at a location spaced below the crown end in a travel path of the traveling block at that location comprising support beams secured to said crown end, a plate secured to said support beams and a bumper pad secured to said plate; driving the traveling block up the derrick until just before it contacts the bumper pad; and applying the brakes to stop the traveling block.